Quantum Dynamics of Electronic Excitations in Biomolecular Chromophores: Role of the Protein Environment and Solvent

Gilmore, J.B. and McKenzie, R.H. (2008) Quantum Dynamics of Electronic Excitations in Biomolecular Chromophores: Role of the Protein Environment and Solvent. The Journal of Physical Chemistry A, 112 11: 2162-2176. doi:10.1021/jp710243t


Author Gilmore, J.B.
McKenzie, R.H.
Title Quantum Dynamics of Electronic Excitations in Biomolecular Chromophores: Role of the Protein Environment and Solvent
Journal name The Journal of Physical Chemistry A   Check publisher's open access policy
ISSN 1089-5639
Publication date 2008-03-20
Year available 2008
Sub-type Critical review of research, literature review, critical commentary
DOI 10.1021/jp710243t
Open Access Status Not yet assessed
Volume 112
Issue 11
Start page 2162
End page 2176
Total pages 15
Editor Schatz, G.C.
Gruebele, M.
Place of publication United States
Publisher American Chemical Society
Language eng
Subject C1
970102 Expanding Knowledge in the Physical Sciences
029999 Physical Sciences not elsewhere classified
Abstract A biomolecular chromophore can be viewed as a quantum system with a small number of degrees of freedom interacting with an environment (the surrounding protein and solvent) which has many degrees of freedom, the majority of which can be described classically. The system−environment interaction can be described by a spectral density for a spin−boson model. The quantum dynamics of electronic excitations in the chromophore are completely determined by this spectral density, which is of great interest for describing quantum decoherence and quantum measurements. Specifically, the spectral density determines the time scale for the “collapse” of the wave function of the chromophore due to continuous measurement of its quantum state by the environment. Although of fundamental interest, there very few physical systems for which the spectral density has been determined experimentally and characterized. In contrast, here, we give the parameters for the spectral densities for a wide range of chromophores, proteins, and solvents. Expressions for the spectral density are derived for continuum dielectric models of the chromophore environment. There are contributions to the spectral density from each component of the environment: the protein, the water bound to the protein, and the bulk solvent. Each component affects the quantum dynamics of the chromophore on distinctly different time scales. Our results provide a natural description of the different time scales observed in ultrafast laser spectroscopy, including three pulse photon echo decay and dynamic Stokes shift measurements. We show that even if the chromophore is well separated from the solvent by the surrounding protein, ultrafast solvation can be still be dominated by the solvent. Consequently, we suggest that the subpicosecond solvation observed in some biomolecular chromophores should not necessarily be assigned to ultrafast protein dynamics. The magnitude of the chromophore−environment coupling is sufficiently strong that the quantum dynamics of electronic excitations in most chromophores at room temperature is incoherent, and the time scale for “collapse” of the wave function is typically less than 10 fs.
Keyword Chemistry, Physical
Physics, Atomic, Molecular & Chemical
Chemistry
Physics
CHEMISTRY, PHYSICAL
PHYSICS, ATOMIC, MOLECULAR & CHEMICAL
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Critical review of research, literature review, critical commentary
Collections: 2009 Higher Education Research Data Collection
School of Mathematics and Physics
 
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Created: Wed, 01 Apr 2009, 00:40:29 EST by Jo Hughes on behalf of School of Mathematics & Physics